Method and apparatus for isolating a cogeneration system from a utility source

Abstract

A cogeneration system is provided that includes at least one generator and a controller. The controller is in electrical communication with the at least one generator. The controller is structured to transmit a signal to the at least one generator to cause the at least one generator to change by a predetermined amount the frequency and/or voltage of the output power from the at least one generator to enable an interruption of the utility source to be detected so that the at least one generator can be isolated from the utility source.

What is claimed is:  
     
         1 . An apparatus for isolating a utility-interconnected generator from a utility source, comprising: 
 a controller, said controller being structured to transmit a signal to the generator to cause the generator to change by a predetermined amount at least one of the frequency and voltage of the output power from the generator to thereby enable the detection of a utility source interruption and the isolation of the generator from the utility source due to at least one of overfrequency, overvoltage, underfrequency, and undervoltage.    
     
     
         2 . An apparatus according to  claim 1  wherein said controller is structured to periodically transmit the signal to the generator.  
     
     
         3 . An apparatus according to  claim 1  wherein said controller comprises a programmable logic controller.  
     
     
         4 . An apparatus according to  claim 1  wherein said controller comprises a microprocessor.  
     
     
         5 . An apparatus according to  claim 1  wherein said controller comprises a solid-state reference adjuster.  
     
     
         6 . An apparatus according to  claim 1  where said controller comprises a transistor network.  
     
     
         7 . A utility-interconnected cogeneration system, comprising: 
 at least one generator; and    a controller, said controller being in electrical communication with said at least one generator, said controller being structured to transmit a signal to said at least one generator to cause said at least one generator to change by a predetermined amount at least one of the frequency and voltage of the output power from said at least one generator to thereby enable the detection of a utility source interruption and the isolation of the generator from the utility source due to at least one of overfrequency, overvoltage, underfrequency, and undervoltage.    
     
     
         8 . An apparatus according to  claim 7  wherein said controller is structured to periodically transmit the signal to the generator.  
     
     
         9 . An apparatus according to  claim 7  wherein said controller comprises a programmable logic controller.  
     
     
         10 . An apparatus according to  claim 7  wherein said controller comprises a microprocessor.  
     
     
         11 . An apparatus according to  claim 7  wherein said controller comprises a solid-state reference adjuster.  
     
     
         12 . An apparatus according to  claim 7  where said controller comprises a transistor network.  
     
     
         13 . A method of monitoring a utility source, comprising: 
 transmitting a signal from a controller to a generator to cause the generator to change by a predetermined amount at least one of the frequency and voltage of the output power from the generator; and    detecting the interruption of the utility source.    
     
     
         14 . A method according to  claim 13  further comprising periodically repeating said transmitting step.  
     
     
         15 . A method according to  claim 13  wherein said detecting step comprises sensing at least one of overvoltage and undervoltage.  
     
     
         16 . A method according to  claim 13  wherein said detecting step comprises sensing at least one of overfrequency and underfrequency.  
     
     
         17 . A method of detecting the interruption of a utility source and isolating a utility-interconnected generator, comprising: 
 transmitting a signal from a controller to a generator to cause the generator to change by a predetermined amount at least one of the frequency and voltage of the output power from the generator;    detecting an interruption of the utility source; and    subsequent to said detecting step, opening a circuit breaker between the generator and the utility source to isolate the generator from the utility source.    
     
     
         18 . A method according to  claim 17  wherein said detecting step comprises sensing with a protective relay at least one of overfrequency and underfrequency.  
     
     
         19 . A method according to  claim 17  wherein said detecting step comprises sensing with a protective relay at least one of overvoltage and undervoltage.  
     
     
         20 . A method according to  claim 18  further comprising periodically repeating said transmitting step.